If you want the duration of the clip to grow according to the playback speed, you want to use Time Stretch rather than Time Remap.
Time Remapping allows you to have variable playback speed along the layer's duration (AE does allow you to extend or contract the duration of a time remapped layer, but it's not a direct consequence of applying it). You can think of Time remapping as the ability to animate a virtual playhead from point to point (forward or backwards) in the layer's source content.
Time Streteching is a more conventional way of modifying duration by adjusting the playback speed (including reverse playback, etc).
For more information, see Time-stretching and time-remapping in After Effects Help.
Thanks for the reply. I did experiment with time stretch and it did work like you said, but has limited applicability because it works with the whole layer rather than just part of it. Also, it has completely no options whereas the time remap is full of features. Could you explain how to extend the duration of a time remapped layer?
Well since those instructions didn't explain it very well, I'll tell anyone interested. All you have to do is go to layer>enable time remapping and then your able to grab the handle on the clip and expand or contract it. I didn't see that in the link you gave.
Oceanking, I think this is described well in the Help page Todd linked to (with a picture that shows how to drag the ends of the layer bars).
Here's the relevant paragraph:
Trim or extend layers in the Timeline panel
- Select one or more layers in the Timeline panel.
- Do one of the following:
Drag either end of a layer duration bar.
Move the current-time indicator to the time at which you want to set the In point or Out point. To set the In point to the current time, press Alt+[ (Windows) or Option+[ (Mac OS). To set the Out point to the current time, press Alt+] (Windows) or Option+] (Mac OS).
I personally think the second method provides a much larger degree of precision and convenience (and you can perform that operation with as many layers as you want, at the same time).
So, for example, suppose you want a layer (or a dozen layers - same thing, time remapped or not) to be exactly 4 seconds longer. You could achieve this very quckly:
1. With your desired layer selected, press "O" so you're sure go to the out point of your layer, without any guesswork.
3. If you press Command+Shift+J (Mac) or Control+Shift+J (Win), the "Go to Time" dialog appears. Type "+4.". This means send the Current Time Indicator to a place which is current time + 4 and the dot (".") means "00", so it's "4:00" (four seconds).
4. Press Option+] (Mac) or Alt+] (Win) to make the layer out point extend towards the Current Time Indicator.
You can do this with as many layers selected as you like, so it's very powerful.
If you attempted to do the same by dragging the ends of the layer bars, you could be dragging around for a long time
And with less precission of course.
Of course, footage layers (ie, video) which are not time remapped will have a limit imposed by the original source frames.
Solid, Shape, Text, Null, Adjustment, imported graphics and time remapped layers can be freely trimmed/extended.